1. Field of the Invention
The present invention relates to a gamma voltage generator, and more particularly, to a gamma voltage generator which can generate gamma voltages to be independently applied to RGB (red, green and blue) image signals and a digital-to-analog converter (DAC) having the same.
2. Description of the Related Art
In general, gamma correction is a task of correcting the different photoelectrical conversion characteristics and the nonlinearity of a camera and a receiver when converting light into electrical signals in the camera and reconverting the converted electrical signals into an image in the receiver. A mathematical expression applied when implementing the gamma correction can be shown as a curve, and this curve is called a gamma curve.
In order to implement gamma correction, a plurality of gamma voltages having predetermined voltage levels are set and used. Since the gamma voltages vary depending upon the characteristics of a display, the voltage levels of the gamma voltages should be controlled, which is called gamma control. The gamma control means that, when two data having different maximum luminances are normalized or tuned to be within the same range, a maximum luminance and a minimum luminance as two vertexes are maintained as they are and only the slopes of luminance curves are changed so that colors of intermediate tones become more dark or light. The gamma voltages are used in the gamma control.
FIG. 1 shows the transmittances of RGB image signals with respect to gray scale.
Referring to FIG. 1, the transmittances of red (R), green (G) and blue (B) image signals are different in a region (indicated by a dotted ellipse) where gray scale is large. This is because a gray voltage is commonly applied to all of the RGB image signals. The difference causes limitations in reproducing an original color.
FIG. 2 is a circuit diagram of a conventional gamma voltage generator.
Referring to FIG. 2, a gamma voltage generator 200 is realized by an array of a plurality of resistors which are connected in series between inputted gamma reference voltages having a plurality of voltage levels. The intermediate node vales of the array of resistors correspond to the gray scale shown in FIG. 1.
FIG. 3 is a block diagram illustrating a DAC for outputting gamma voltages corresponding to gamma voltage selection signals.
Referring to FIG. 3, a DAC 300 includes a gamma voltage generator 310 and a gamma voltage selection block 320.
The gamma voltage generator 310 generates gamma voltages having the number the same as to or less than 2N (N is an integer), using inputted gamma reference voltages. The gamma voltage selection block 320 selects and outputs gamma voltages VG corresponding to N-bit gamma voltage selection signals D<0:N−1> among the 2N number of gamma voltages.
As shown in FIG. 1, the transmittances of RGB image signals are different in the region (indicated by a dotted ellipse) where gray scale is large. In this regard, disadvantages are caused in that the gamma voltage generator 310 shown in FIG. 3, using the circuit shown in FIG. 2, cannot precisely control the differences.